Implicit Solvent Models - Computational
Approaches to Solvation
Suppose that we were to average out the effects of all of the solvent
molecules, effectively integrating over the coordinates describing the
solvent molecules.
This would dramatically simplify the description of the solvent
molecules, and thereby simplify the computation of the energy of the
solute–solvent system.
This is the general principle behind the implicit solvent models.
The solvent is described by a single term, its dielectric constant, and we
just need to treat the interaction of the solute with this field.
The implicit solvation model begins by creating a cavity inside the
polarizable medium to hold the solute molecule.
There is an energy cost for cavitation, ∆Gcav, due to solvent–solvent
interactions that are removed.
The solute is then placed into the cavity, resulting in electrostatic and
non-electrostatic interactions between the solute and the polarizable
medium.
The solute induces a polarization of the dielectric medium, and the
medium induces a polarization upon the solute.
The electrostatic contribution, ∆Gelec, takes into account these attractive
terms along with the energetic cost of polarizing the solute and solvent.
The main non electrostatic contribution to the solvation energy, ∆G non-elec,
is dispersion, but other factors may come into play such as the non-
electrostatic component of hydrogen bonding.
The total solvation energy is then a sum of these three energetic
contributions:
∆Gsolvation = ∆Gelec + ∆Gcav + ∆Gnon-elec
The Poisson equation describes the electrostatics of a dielectric medium
with an embedded charged species;
where F(r) is the the electric field perpendicular to the cavity , σ(r ) is the
charge density at point r on the surface of the cavity.
If the solute carries a nonzero charge, the Poisson–Boltzmann equation
applies.
Approaches to Solvation
Suppose that we were to average out the effects of all of the solvent
molecules, effectively integrating over the coordinates describing the
solvent molecules.
This would dramatically simplify the description of the solvent
molecules, and thereby simplify the computation of the energy of the
solute–solvent system.
This is the general principle behind the implicit solvent models.
The solvent is described by a single term, its dielectric constant, and we
just need to treat the interaction of the solute with this field.
The implicit solvation model begins by creating a cavity inside the
polarizable medium to hold the solute molecule.
There is an energy cost for cavitation, ∆Gcav, due to solvent–solvent
interactions that are removed.
The solute is then placed into the cavity, resulting in electrostatic and
non-electrostatic interactions between the solute and the polarizable
medium.
The solute induces a polarization of the dielectric medium, and the
medium induces a polarization upon the solute.
The electrostatic contribution, ∆Gelec, takes into account these attractive
terms along with the energetic cost of polarizing the solute and solvent.
The main non electrostatic contribution to the solvation energy, ∆G non-elec,
is dispersion, but other factors may come into play such as the non-
electrostatic component of hydrogen bonding.
The total solvation energy is then a sum of these three energetic
contributions:
∆Gsolvation = ∆Gelec + ∆Gcav + ∆Gnon-elec
The Poisson equation describes the electrostatics of a dielectric medium
with an embedded charged species;
where F(r) is the the electric field perpendicular to the cavity , σ(r ) is the
charge density at point r on the surface of the cavity.
If the solute carries a nonzero charge, the Poisson–Boltzmann equation
applies.
